import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;
//感觉是最大差距的一半，而计算最大差距需要把a[i]进行排序

public class aa{
    public static void main(String[] arg){
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int l=sc.nextInt();
        ArrayList<Integer> a=new ArrayList<>(n);
        for(int i=0;i<n;i++){
            a.add(sc.nextInt());
        }
        Collections.sort(a);
        int maxDiff=0;
        for(int i=1;i<n;i++){
            int curDiff=a.get(i)-a.get(i-1);
            if(maxDiff<curDiff){
                maxDiff=curDiff;
            }
        }
        maxDiff=Math.max(maxDiff,2*a.get(0));
        maxDiff=Math.max(maxDiff,2*(l-a.get(n-1)));
        System.out.println(String.format("%.2f",(double)maxDiff/2));
    }
}
